No ligatures in syllable with the style tags using LuaLaTeX

[rpspringuel]

As reported here by Sr. Maria Ruth:

In GregorioTeX 5.1.1, when a style tag is used just for a part of a syllable, part that corresponds to a ligature, LuaLaTeX never typesets the ligature [liga_lualatex_1], while LuaTeX does, with the exception of <c> and <ul> [liga_luatex]. In "gregoriotex.sty", the macros \GreItalic, \GreSmallCaps, \GreBold, and \GreTypewriter use \textit, \textsc, \textbf, and \texttt in their definition. I think those LaTeX's control sequences should be replaced by \itshape, \scshape, \bfseries, and \ttfamily because they cut off (they armour) each character in the ligature, while the last ones do not [liga_lualatex_2].

Anyway I think the overall procedure which manages the style tags within a syllable should be improved.

liga_issues.zip

[rpspringuel]

The proposed fix works for bold and italics. The sample for small capitals and typewriter is inconclusive because no ligature is involved.

\underline does not have a flag equivalent in normal LaTeX. To fix it for this case we would need to test the various packages which improve underlining and add that dependency.

Color is already a switch, but its doing something that already breaks the ligature. Based on this answer it appears that we need to switch from xcolor to luacolor to make this work. Is switching this dependency acceptable?

[rpspringuel]

Correction. We would need to load luacolor in addition to xcolor, not instead of it.

[rpspringuel]

Additional correction: the luacolor solution only works for LuaLaTeX. The package doesn't appear to be compatible with LuaTeX, so I'm looking for an additional option.

[rpspringuel]

After further reflection, I cannot come up with a situation where small capitals or typewriter would actually make use of ligatures. As a result, while will make the change according to the pattern for the ones which are problematic, I'm not going to worry about testing it at this point.

I've looked at the soul and ulem packages, neither provide the needed fix for underlining. I'm looking for other options.

Finally, the luacolor package seems to be breaking cavum shapes. I'm still investigating as to why.

[rpspringuel]

I've got a partial fix for the color issue. It works on cavum shapes but is having difficulties with alterations. Specifically, alterations attached to a custos or clef change get filled with black (the color change to grebackgroundcolor is not being applied) while other alterations are fine. Anyone have any ideas as to why those two situations would end up with the different hole filling results? I've been attempting to backtrace without success at this point. Take a look at d323979 to see where I'm at so far.

[rpspringuel]

I was able to boil it down and it comes to color changes not happening inside \discretionary when luacolor is loaded. I've posted another question looking for a way to fix this.